1. Field of the Invention
This invention relates to downhole measurement tools having a regulated voltage power supply and method of use thereof, and more particular relates to downhole measurement tools associated with electrical submersible pumps (ESPs) for providing a stabilization technique for a five (5) volt power supply over a wide temperature range.
2. Description of the Related Art
Various types of downhole equipment, such as pumps and similar devices, are used to move fluids from beneath the surface of the earth to the surface. Well known applications include oil and gas wells and water wells. A typical downhole arrangement would include a string composed of a series of tubes or tubing suspended from the surface. One type of well-known pump is a downhole electrical submersible pump. The electrical submersible pump either includes or is connected to a downhole motor which is sealed so that the whole assembly is submerged in the fluid to be pumped. The downhole motor is connected to a three-phase power source at the surface and operates beneath the level of fluid downhole in order to pump the fluid to the surface.
In the common design of many downhole measurement tools associated with an electrical submersible pump, they are connected to the Y-point of the downhole motor of the electrical submersible pump and to the electrical ground of the downhole system. The three-phase power supply for the electrical submersible pump is isolated from the electrical ground, and the downhole measurement tool utilizes this feature to communicate to an associated surface equipment of a downhole system by low frequency modulation of a current or voltage supplied by the associated surface equipment. The downhole measurement tool is coupled to the electrical submersible pump and used to monitor certain downhole parameters, such as pressure and temperature, of a subterranean bore-hole.
With the various protective mechanisms in place, and the several thousand feet of cable involved, the DC voltage supplied to the downhole measurement tool may vary from about nine (9) to about one-hundred (100) volts as information is sent back to the surface equipment from the downhole measurement tool. As the downhole measurement tool is subjected to higher temperature environments, the increased temperature exceeds the operational capabilities of the internal circuitry of most currently available five (5) volt regulator devices. While some specially-graded or designed five (5) volt regulators are available for such high temperature environments, these regulators are extremely expensive compared to low temperature five (5) voltage regulators.
Since the DC current requirements for the circuitry in the downhole measurement tool is relatively low between about eight (8) and twelve (12) milliamps, and can be allowed to vary by about 5%, discrete devices, i.e. transistors, Zener diodes, and resistors, can be used to provide a five (5) volt supply at the required temperature; however, the temperature coefficient of the forward-biased PN junction voltages involved prohibits good voltage regulation over the temperature range from about 25° C. to about 175° C.
It is therefore desirable to provide downhole measurement tools having an improved regulated voltage power supply and method of use thereof.
It is further desirable to provide downhole measurement tools associated with ESPs that provide a stabilization technique for a five (5) volt power supply over a wide range of operating temperatures.
It is still further desirable to provide a five (5) volt regulator circuit for downhole measurement tools, which is low cost and provides better voltage regulation than is achieved with the standard discrete-device voltage regulator circuits.
It is yet further desirable to provide a voltage regulator circuit for downhole measurement tools having a temperature dependent resistance to adjust the feedback of the regulated voltage to compensate for the temperature coefficient effects of the other components in the regulator circuit.
Other advantages and features of the invention will be apparent from the following description and from the claims.